1. Field of the Invention
The present invention relates to clinical screening techniques for identifying cognitive impairment and, more particularly, to a non-invasive system and method for quantitative screening for mild traumatic brain injury (mTBI) and other neurological disorders by evaluating the intra-individual variability (IIV) of motor performance.
2. Description of Prior Art
In many activities, overall performance is dependent on a high level of cognitive performance. However, there are certain forms of mild cognitive impairment (MCI) that can compromise performance, including mild traumatic brain injury (mTBI), early Alzheimer's disease, post-traumatic stress disorder (PTSD), intoxication, and sleep deprivation.
mTBI is particularly common in the military and athletic settings. The onset of mTBI is very subtle, and yet it can have serious consequences if left undetected and untreated. Detecting mTBI is very difficult because the symptoms are not always manifest. An individual may be superficially functioning quite well day-to-day, continuing to work, and apparently not restricted in any daily activity. Moreover, individuals exhibit different signs and symptoms, the functional consequences appear gradually, and no specific test has been developed for diagnosis. The gold standard method of assessing mTBI is to perform a detailed neurological evaluation, extensive cognitive testing, and imaging. This traditional approach imposes undesirable costs and delays and is impractical on the playing field, battle field (for forwardly deployed military personnel), or on the jobsite. Consequently, in some situations there is a significant need to screen individuals for mild cognitive impairment to ensure that they are capable of performing certain tasks safely without risk to themselves or others, or that a degenerative condition does not exist.
The armed services in particular have a long-felt need to assess mild traumatic brain injury (mTBI) which can arise from injuries by explosions or the like or from PTSD. The cognitive and motor hallmarks of mTBI include psychomotor slowing, poor concentration and attention retrieval resulting in increased variability of performance, and overall executive dysfunction. Stuss et al., Adult Clinical Neuropsychology: Lessons from Studies of the Frontal Lobes, Annual Review of Psychology, 53, 401-433 (2003). Previous work has shown that these features are manifest in both cognitive function and motor performance, reaction time and performance reliability. Walker et al., Motor Impairment After Severe Traumatic Brain Injury: A Longitudinal Multicenter Study, Jnl of Rehabilitation Research & Development, vl 44, no. 7, pp 975-982 (2007). Also, Sosnoff, Broglio & Ferrara suggest that mTBI reduces motor control especially when visual information is utilized. Sosnoff, J. J. et al., Previous Mild Traumatic Brain Injury And Postural-Control Dynamics, Jnl of Athletic Training. 46(1), 85-91 (2011). Furthermore, clinical motor/psychomotor evaluations (tests of balance and coordination) are sensitive to mild cognitive impairment. See, e.g., Kluger et al., Clinical Features of MCI: Motor Changes, International Psychogeriatrics, February; 20 (1): 32-39 (2008). Work-related manifestations include slower reaction time, headaches, irritability, memory impairments, and sleep difficulty. These symptoms result in decreased performance of far-forward troops, where performance is critical to mission effectiveness and safety. The military seeks to assess this not only to determine who has sustained an injury, but also their recovery trajectory in order to predict return to duty, and also to detect malingering by those who feign mTBI to gain an early discharge. As a result, there is a major cognitive assessment initiative for Service Members. In 2008 the Assistant Secretary of Defense, Health Affairs office, directed all Services to begin implementing baseline pre-deployment neurocognitive assessments for all Service members. Their original goal was to establish a baseline in the event that the Service member becomes injured or is exposed to a traumatic brain injury (TBI), so that subsequent test results can be compared to the original baseline to determine the extent of MCI and treatment options. An automated tool was developed to collect the baseline information on attention, memory, and thinking ability. The tool, the Automated Neuropsychological Assessment Metrics (ANAM®) test system consists of a library of computer-based tests that include neuropsychology, readiness to perform, neurotoxicology, pharmacology, and human factors research. Other neuropsychological tests include the Trail Making Test (a paper and pencil test in which the subject is instructed to connect a set of 25 dots as fast as possible while still maintaining accuracy), screening interviews such as the Military Acute Concussion Evaluation (MACE), and computerized cognitive tests such as the Automated Neuropsychological Assessment Metrics (ANAM), ImPACT, and a variety of other computerized tests. The existing MACE screening tool and the ANAM battery are the current assessments used to evaluate mTBI. Defense and Veterans Brain Injury Center (DVBIC), Clinical Practice Guidelines and Recommendations, Working Group on the Acute Management of Mild Traumatic Brain Injury in Military Operational Settings (2006). Both tools represent the culmination of years of work by the military. Schwab, K, A. et al., Screening For Traumatic Brain Injury In Troops Returning From Deployment In Afghanistan And Iraq: Initial Investigation of The Usefulness of a Short Screening Tool For Traumatic Brain Injury, Jnl of Head Trauma Rehabilitation, 22, 377-389 (2007). However, both tools take considerable time and require professionally trained testers. The deficiencies in the sensitivity and specificity of these tests to mTBI have been well documented.
More recently, it has been suggested that mTBI affects attention and impairs the anticipatory process. There is a distinct relationship between attention and motor performance variability. Specifically, mTBI patients show an increase in the degree to which their performance varies from trial to trial. Jamshid Ghajar, The Predictive Brain State: Timing Deficiency in Traumatic Brain Injury?, Neurorehabil Neural Repair May/June 2008 vol, 22 no. 3 217-227.
Although it is currently possible to measure and monitor motor performance variability in a clinical setting, there is no existing standardized method or system for doing so in the field. Therefore, military medical specialists and other far-forward personnel have no means to assess mTBI. The present inventors have developed a method and system to assess intra-individual response variability (IIV) as manifested in a simple motor task (for example, tracking visual targets) that is an effective mTBI screen and, either alone or in combination with one or more other assessments, potentially a test for diagnosing mTBI or other cognitive impairments such as brain damage, concussion and/or dementia. It is also directly relevant to the athletic setting, and settings where sleep deprivation or intoxication may require detection. The proposed method and system is simple, quantitative, noninvasive, and suitable for use in any environment by any personnel at all echelons of care.